Andy Murray produced his most accomplished performance of the season but came up short against the resilience of world No.1 Novak Djokovic, who won 7-6(1) 6-7(1) 6-2 6-4 to book his spot in the semi-finals of the US Open.

Murray, who beat Djokovic to claim his first grand slam title in New York two years ago and again to win Wimbledon in 2013, went toe-to-toe with the seven-time grand slam champion for two and a half sets, firing his forehand with a rare ferocity.

Murray: I couldn't match his strength

Andy Murray avoided another bout of cramp but said he just could not match Novak Djokovic's fitness in the latter stages of their quarter-final.

The world No.9, who beat Djokovic over five sets and four hours to claim his first grand slam in New York in 2012, faded in the third and fourth sets as he struggled with stiffness in his back and hips.

Ultimately, Djokovic's fitness in the latter stages and clinical ruthlessness throughout the contest proved decisive; at the end of the three-hour, 32 minute quarter-final, Murray had claimed four breaks from 19 opportunities; the Serbian seven from 10.

"We both gave our best," Djokovic said in his on-court interview. "At times the tennis was not that nice - we made a lot of unforced errors - but that's because of the physical battle we played for two and a half sets. I knew the more aggressive one would win it - I'm glad I stayed fit and managed to come through."

Murray broke in the opening game but failed to consolidate, Djokovic teasing the break back after eight minutes of cat-and-mouse tennis that set the tone for the match. A second break for the Serbian soon after put him 4-1 ahead, but Murray hit back to level up at 4-4, at which point both players found another gear.

One 29-shot rally brought the crowd to their feet as both men battled to 6-6 but Murray produced a horror show in the tiebreak, firing a double-fault and a string of wild drives to fall a set behind after 73 minutes.

The hangover carried into the second set as Murray, far too loose, was broken to 15 to trail 2-1. It proved infectious: Djokovic fell to the odd break in three at the midpoint of the set before both men found their feet again at 4-4.

It was Djokovic's turn to disappear in the ensuing tiebreak but the world No.1 returned with a vengeance in the third set, claiming another couple of breaks that this time went unanswered, despite Murray's chances to break back while trailing 3-1.

As the match passed the three-hour mark shortly before 1am, Murray's movement became laboured and the zip faded from his serve. Djokovic, also showing glimpses of slowing down, did what he could to run Murray ragged but could not take advantage on the scoreboard as the Scot continued to strike the ball sweetly and keep the points short.

Serving to stay in the match, however, and with a spectator heckling him mid-delivery, Murray folded, netting a backhand on Djokovic's first match point to fall to his 13th defeat against the Serbian in 21 meetings.

The pair ended with 93 winners combined, Murray shading Djokovic 47 to 46, but the Scot's 65 unforced errors proved critical, with Djokovic giving up 48 in four sets.

Up next for the No.1 seed is Kei Nishikori, who overcame weary limbs, a swift turnaround and a second top-five seed in succession to book his place in his first grand slam semi-final, beating Australian Open champion Stan Wawrinka 3-6 7-5 7-6(9) 6-7(5) 6-4.

Less than 48 hours after beating Milos Raonic in a match that ended at 2.26am EST - a joint-record late finish at Flushing Meadows - the No.10 seed once again went beyond the four-hour barrier to become the first Japanese man to reach the US Open semi-finals since 1918.

"I had a little bit jet lag today," Nishikori joked after getting to bed at 6am on Tuesday morning. "My body was tight. I was a little bit tired yesterday, but today was almost, not 100% but close to feeling pretty good my body. It's great for my confidence."

After enduring a tricky start to his Manchester United career, perhaps it is fair that Marcos Rojo celebrated so boisterously as he watched his first professional club Estudiantes beat fierce rivals Gimnasia